This invention relates to an electromagnetic wave shielding material which can effectively prevent radiation or intrusion of electromagnetic waves therethrough.
Precision electronic appliances including computers often suffer wave interference to malfunction and runaway in response to external electromagnetic waves such as impulsive noises. As a preventive measure for such wave interference, it has been suggested to form a shielding film on the internal wall surfaces of the resin cases of these electric appliances including computers by applying a nickel coating or one containing carbon or a metal powder in order to impart electric conductivity to said wall surfaces.
However, in the above method, the internal surface of such resin case comprising a molded product made of plastic and the like is found to have considerable roughness by microscopic observation, so that the shielding film can be formed only thinly especially at those portions with radii and on the rising faces, making it generally very difficult to form a uniform film over the entire internal surface of the case. Accordingly, if the formed shielding film is too thin, sufficient shielding effect may not be obtained. Further, the shielding coating may peel during a long period and the peeled metallic debris may drop on the IC substrate to cause drop in insulating properties, causing malfunction in the electronic appliances.